1. Field of the Invention
The present invention relates to a feedback control system which controls the output of a controlled object according to a control variable command.
2. Description of the Related Art
Feedback control has so far been applied to control the output of a controlled object in response to each of control variable commands. The control computation unit devised to undertake feedback control renders service in two different types--an analog computation type using an operational amplifier, and a digital computation type wherein a microcomputer or the like is utilized. Feedback control through analog computation is characterized by serial control computation in response to the command of a controlled variable or the signal thereof to be feedback. In view of this, analog computation-combined feedback control is otherwise called a continuous-time system. Meanwhile, digital computation-introduced feedback control is implemented via control computation in response to the signal sampled at a certain interval of time out of some controlled variable signals. Therefore, the latter feedback control is referred to as sampled data system control.
A continuous-time system undergoes an inconvenience in that the time required before the controlled output gets settled after the occurrence of a control variable command fluctuation and/or a disturbance, that is, the settling time, is long. Meanwhile, the control referred to above provides an advantage that the response characteristic thereof is hardly subject to change regardless of parametral fluctuations of a controlled object.
Now, with sampled data control, it is practical to settle the controlled variable within a finite time. However, the control remarked above concurs with a stepwise change of a manipulated variable, whereby an unfavorable consequence is brought about to the controlled object involved. Assuming the case of motor control, if there is witnessed a large magnitude in the stepwise change of a manipulated variable command, a machine, the load coupled to the motor concerned will experience intensive shocks.
Further, with sampled data control, control computation is effected, following the signal just sampled by a sampler. Such being the case, if the signal from a control variable detector for feeding back the control variable at the instant of signal sampling comes to carry noises (external disturbance), control performance is affected greatly by the disturbance.
Furthermore, where integral gain Ki, proportional gain Kp, and so forth of the control computation unit are optimally selected for the controlled object involved, it is feasible to settle the controlled variable within a finite time. But in the event the proper relationship between a selected control gain and the controlled object concerned is lost due to some change on the part of the controlled system, controllability declines greatly, let alone becoming incapable of showing a finite time-settling response.
To cope with the above-quoted problem, it is conceivable that the interval of sampling is decreased so that the controlled variable will be settled through a relatively large number of samplings, thereby to fabricate such a control system robust against parametral fluctuations of the controlled object involved. This, however, results in rendering the control computation unit configuration complex, with the number of parameters (gains) requiring adjustment within the control computation unit being increased. Moreover, such a system will therefore not allow ease of realization.